This invention relates to a sewage treatment system and more particularly to a means and method for achieving aerobic digestion. Embodiments feature improved oxygenation and, at the same time, an improved and most rapid separation of the solids and the liquid content of the sewage. The invention is equally applicable to a sanitary system for a single residence, for a mobile home and for a complete community.
U.S. Pat. Nos. 3,925,208, 3,879,285 and 3,817,858 represent the most pertinent of the prior art of which those involved in the preparation of this disclosure are aware. Apart from the specifics of these patents, there have been many other proposals the objectives of which have been improvements in the field of aerobic digestion. None, however, have offered a sewage treatment system wherein there is (a) as effective an application and utilization of oxygen; (b) such a rapid separation and settling out of contained solids in a first phase treatment of raw sewage; (c) such a reduction of power requirements; and (d) the capability of achieving as clear and as potable a water product in a relatively brief interval of time as enabled by the present invention.
Further, in using conventional sewage treatment systems employing principles of aerobic digestion, it has proven to be extremely difficult, without extended and expensive treatment procedures to obtain potable water wherein visible suspended solids have virtually been eliminated. Nor has it been easy to reduce the solids embodied in sewage to a form facilitating their disposal and/or utilization.
The following examples illustrate some of the difficulties experienced in operation of conventional sewage treatment systems utilizing principles of aerobic digestion. The difficulties stem primarily from the manner in which efforts are made to expose the solids in the sewage to oxygen.
In one type of prior art system the sewage is delivered to a settling tank by way of relatively elevated nozzles, the theory being that in this way the sewage solids will be exposed to air as they drop into the tank, thereby to achieve oxygenation. A basic problem in this procedure is that the solids frequently crust and clog the delivery nozzles. The maintenance cost and down time resulting are of course obvious and the oxygenation is less than necessary to satisfy environmental needs. Also this system does not adequately achieve a separation of suspended solids from the water content of the sewage.
In another type of sewage treatment system "bubblers" are employed to drive air up and through a body of sewage. This arrangement tends to churn the sewage and to keep solids in suspension and consumes a lot of power. Moreover, when air is turned off the bubblers clog with the sewage in which they are immersed.
A third type applies a plurality of jets of air to the surface of a body of sewage in a fully enclosed chamber. The air nozzles are in this case positioned at levels above the upper surface of the sewage and directed down in an effort to produce an adequate infusion of oxygen. The rate of oxygenation in this case has proven to be insufficient to achieve the desired results. It has been proposed in using this type of system to induce circular flow patterns in the sewage surface to facilitate digestion but this also has not been found satisfactory.
There have been other systems but, as the foregoing, each has shown a serious deficiency and none have fully met environmental standards such as now required.